The background description provided herein is for the purpose of generally presenting the context of the present invention. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely as a result of its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art. The subject matter in the background of the invention section merely represents different approaches, which in and of themselves may also be inventions.
The optical fiber communication has been widely used in long distance backbone networks to metropolitan area networks and access networks, due to features such as large capacity, long transfer distance, fast transfer speed, and cost saving. The development of the optical fiber communication technology has always been aimed at faster transfer speed, larger capacity, and longer transfer distance, and continuously promotes and improves the performance indexes of an optical fiber and the communication technology of the optical fiber. Especially, in recent years, with the explosive growth in the volume of IP services, the communication network starts to head towards a next generation of sustainable development, and a constructed optical fiber infrastructure having a huge transfer capacity and long distance is the physical basis of the next generation of networks. To satisfy development requirements of the optical fiber communication system, relevant performance indexes of the optical fiber as a transfer medium of an optical fiber communication network also needs to be further improved.
The attenuation coefficient of an optical fiber of one of important performance indexes of the optical fiber, to which the relay distance of the optical fiber communication majorly depends. A small attenuation coefficient of an optical fiber indicates a long distance for which an optical signal carried in the optical fiber can be transferred, and indicates a small attenuation amplitude of a carried optical signal at the same transfer distance. The Optical Signal to Noise Ratio (OSNR) in the optical fiber communication can be effectively increased by reducing the attenuation coefficient, to further improve the transfer quality and the transfer distance of the system. In long-distance transfer distance, an optical signal is transferred by means of relay stations. If the attenuation coefficient of an optical fiber is small, the transfer distance without relay of the optical signal is long, and therefore the distance between relay stations can be increased, thereby greatly reducing the number of relay stations and reducing the operating costs. Therefore, reducing the attenuation coefficient of the optical fiber has a significant meaning in aspects of both system structure optimization and operating costs reduction. In another aspect, with continuously development of FTTX in recent years, it is difficult for the performance of the existing G.652 fiber to meet users' requirements. In an actual application environment, the optical fiber needs to have a particular bending resistance. Therefore, a new generation of bending-insensitive single-mode fiber, G.657 optical fiber, is developed based on the G.652 fiber. The G.657 optical fiber includes a G.657.A optical fiber that is compatible with the G.652 standard and a G.657.B optical fiber that is not compatible with the G.652 standard. The G.657.A type optical fiber has a good compatibility with the G.652.D fiber and has a better bending resistance relative to common G.652.D fibers, and therefore is considered as one of products that are most probably used for replacing the G.652 fiber. Therefore, creation of a new generation of single-mode fiber that is compatible with the G.652 standard, has a low attenuation and a relatively large mode field diameter, and meanwhile also has a bent insensitive property becomes a search focus in the field of communication optical fibers.
Generally, the following several methods may be used to reduce the attenuation of an optical fiber in a manufacturing process of an optical fiber preform. For example, the probability of introduction of external impurities can be reduced by using high-purity raw materials and improving the manufacturing environment and equipment sealing. For example, in Chinese Patent Application No. 201110178833.3, the introduction of external impurities is reduced by using the method of improving the sealing in the process of depositing an optical fiber preform. Alternatively, a process of manufacturing a preform with a larger outer diameter is used, and the over whole attenuation of the optical fiber is reduced by means of the dilution effect of a larger scale perform. In addition, the coating processing used for coating the surface of bare fiber in the process of manufacturing the optical fiber is also a significant factor that influences the attenuation performance of the optical fiber. However, no matter in the aspect of theories or the control of costs and processing in the actual preparation of the optical fiber, reducing doping of the optical fiber and optimizing the cross sections of the optical fiber are the simplest and most effective methods for reducing the attenuation of the optical fiber. Generally, a small concentration of doped material indicates a small loss caused by Rayleigh scattering. In a conventional single-mode fiber, to guarantee total reflection in the optical fiber, a sufficient difference between the refractive indexes of the core layer and the inner cladding layer needs to be ensured, so that the relative refractive index of the core layer is far larger than that of the inner cladding layer of the optical fiber. To ensure such the design, a large amount of doping in a Ge or Ge/F co-doped form needs to be performed in the core layer. However, in the design of cross sections of the conventional optical fiber, laser energy forms a Gaussian distribution in the cross sections of the optical fiber, and approximately 70% laser energy transfers in the core layer with relatively larger doping in the optical fiber. That is, laser transfer of high energy density is centralized in the high-concentration doped core layer having a larger Rayleigh coefficient. By means of proper optical cross section design, a cross section in which energy is not distributed in a Gaussian distribution form is designed, to reduce energy loss in the high-concentration doped core layer, thereby significantly reducing the attenuation performance of the optical fiber.
However, in the conventional cross section design and manufacturing methods for G.657 optical fibers, a relatively large amount of Ge/F co-doping is used in the core layer, and to obtain the optimal macrobending performance, the relative refractive index of the core layer generally is larger than 0.35%. That is, the Ge doping in the core layer is relatively large, thereby causing a relatively large Rayleigh scattering and increasing attenuation of the optical fiber.
Chinese Patent Application No. 201310394404 discloses a design of ultralow attenuation optical fiber, in which the design of an outer cladding layer of pure silica is used. However, a typical step cross section structure is used in the design, instead of using a trench cladding layer design to optimize bending of the optical fiber, and Ge is not used for doping in the core layer thereof, which may therefore cause viscosity mismatch during preparation of the perform. In addition, the attenuation and bending ability thereof are relatively poor.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.